Victims of "land grabbing" have joined 800 of the world's leading environment and development groups to press the UN to establish strong guidelines to protect communities affected by large-scale land investments.

Countries meeting at the UN's Food and Agriculture Organisation in Rome this week are due to adopt a voluntary code on 17 October in response to growing alarm about the scale of international investments being made in poor countries, and the alleged human rights abuses that have followed.

La Via Campesina, Oxfam, Friends of the Earth International and more than 800 other organisations presented a petition against land grabbing to the chair of the FAO's committee on world food security.

"Mounting evidence shows that land grabbing violates human rights and is placing the survival of billions in peril, while corporations and private interests reap the benefits. We urgently need governments to oppose land grabs. They must instead enforce binding human rights instruments and take responsibility for their companies' actions abroad," said Friends of the Earth International's food sovereignty co-ordinator, Kirtana Chandrasekaran. "Ensuring communities access to land and investing in local small-scale food producers is essential to feed the world sustainably in the future."

The EU is leading calls for human rights to be emphasised in the guidelines, but observers said the US was resisting attempts to place too many conditions on large-scale acquisitions.

Faliry Boly, secretary general of Sexagon, a peasant organisation in Mali, said: "Agribusiness projects such as the ones comprising thousands of hectares do great harm and are profoundly illegitimate. We call on parliaments and national governments to immediately cease all massive land grabs current or future and return the plundered land."

The meetings to establish voluntary guidelines take place as a new United Nations Environment Programme (Unep) analysis paper shows that British companies are the third largest investors after China and Saudi Arabia buying, or leasing, more than 1m hectares of land in Ethiopia, Angola, Ghana, Madagascar, Mozambique, Ukraine and Sierra Leone. China has acquired 6.5m hectares, and Saudi Arabia 5.5m.

The paper, from the Unep's global environmental alert service, attributes the rush for land partly to a lack of water in some countries. "The desire to capture water resources to irrigate farmlands has motivated the rush for land," it says. "Middle Eastern states are among the biggest land investors in Africa, driven not by a lack of land, but a lack of water. Between 2004 and 2009 Saudi Arabia leased 376,000 hectares of land in Sudan to grow wheat and rice following declining underground domestic water. China and India have leased thousands of hectares of farmland in Ethiopia; both countries have well-developed irrigation systems but, in the case of China, for example, moving water from the water-rich south to northern China is likely to cost more than leasing land in Africa."

The paper also outlines the potential ecological consequences of large-scale farming and growing biofuel crops. "Monoculture has been widely accepted as the most efficient type of large-scale agriculture," it says. "High yields may result, at least for a time, but growing one crop, such as biofuels, over a large area for several years has a number of negative environmental impacts. Studies in Malaysia and Indonesia have shown that 80%-100% of fauna species in tropical rainforests cannot survive in oil-palm monocultures due to increased pressures from various crop diseases and pests, often requiring large-scale use of chemical pesticides, fungicides and herbicides. In addition, increased fertiliser use to safeguard crop yield may increase pollutant levels in downstream waters and nitrous oxide emissions.

"Semi-mechanised sorghum and sesame production in Sudan illustrates the risks of large-scale farming and holds lessons for current investors. In an agro-ecological environment comparable to Australia, where yields are four tonnes per hectare, sorghum yields are only 0.5 tonnes per hectare and have been stagnant or declining."